1. Field of the Invention
The present invention generally relates to electronic devices and fire protecting mechanisms of the electronic devices. More specifically, the present invention relates to an electronic device where plural electronic circuits are provided in a shelf, the electronic device having a self-extinguishing function, and a fire protecting mechanism of the electronic device.
2. Description of the Related Art
Conventionally, in electronic apparatuses such as communication apparatuses, plural PIUs (plug in unit) where electronic components are mounted on a printed wiring board are received in a shelf. By a Plug-In method using connectors of the PIUs, the PIUs are connected to a back board provided in the shelf so that a single electronic device is formed. Plural electronic devices are stacked in a cabinet on plural steps.
FIG. 1 is a perspective view of a related art electronic device. As shown in FIG. 1, a shelf 1 is provided at a front surface (a surface at an X1 side of FIG. 1) in a related art electronic device 10. In the shelf 1, plural PIUs (Plug In Unit, not shown in FIG. 1) where electronic components such as ICs (Integrated Circuit) or LSIs (Large Scale Integrated circuit) are mounted on a printed wiring board are inserted in an X2 direction in FIG. 1.
At a rear surface (a surface at an X2 side of FIG. 1) of the electronic device 10, a sub-back board 2 is provided outside of a back board 3. Connectors for outside interface are provided on the sub-back board 2.
In addition, the temperature inside of the electronic device 10 is increased due to heat radiated by the electronic components. Accordingly, in order to keep the inside the electronic device 10 at a desirable temperature, fans (not shown in FIG. 1) are provided at a lower part of the electronic device 10 as a forced air cooling part.
By using such fans, air is forcibly taken in from the outside of the electronic device 10 in a Z1 direction of FIG. 1 and made to flow inside the electronic device 10, so that the heated electronic components are cooled. Warmed air is exhausted outside the electronic device 10 via an exhaust opening 4 provided at an upper part of a rear surface (a surface at an X2 side of FIG. 1) of the electronic device 10.
In the meantime, such an electronic apparatus is required to have a self-extinguishing function sufficient to prevent spreading of fire to other electronic devices should a fire break out inside the electronic device. Because of this, in the electronic device 10, in order to prevent the spreading of fire outside the electronic device 10, a punched metal screen 5 is provided at the above-mentioned exhaust opening 4. The punched metal screen 5 is made of a metal plate where a large number of openings are formed. By such a punched metal screen 5, even if a fire breaks out inside the electronic device 10, spreading of the fire outside the electronic device 10 is prevented.
In addition, a foaming coating material, if necessary, is applied to the punched metal screen 5 so that when flames or high temperature gas comes in contact with the punched metal screen 5, the foaming coating material foams. If fire breaks out inside the electronic device 10 so that the temperature becomes a certain number of degrees, the coating material foams and thereby the openings formed in the punched metal screen 5 are closed by the coating material. As a result of this, the spreading of fire outside the electronic device 10 is prevented.
An exhaust opening where a configuration of a temperature fuse can be changed has been suggested in order to prevent use of a low temperature fuse in error when a high temperature fuse should be used. See Japanese Laid-Open Patent Application Publication No. 2001-33089.
Furthermore, a mechanism where a butterfly type tamper is closed by a temperature fuse and a closing spring at the time when fire breaks out has been suggested. See Japanese Laid-Open Patent Application Publication No. 2001-104503.
However, in the related art electronic device 10, the punched metal screen 5 is provided at the exhaust opening 4 for exhausting the air flowing inside the electronic device 10 to the outside. Accordingly, the punched metal screen 5 may obstruct the flow of the air exhausting to outside the electronic device 10. Hence, the punched metal screen 5 may degrade the ability to cool the electronic components generating heats.
In addition, the flow of the air exhausting to outside the electronic device 10 is obstructed by the punched metal screen 5. Therefore, if fire breaks out inside the electronic device 10, high temperature air or unburned flammable gas fills the inside of the electronic device 10 so that it is difficult to extinguish the fire. This may cause to obstruction of the self-extinguishing function.
Furthermore, it is difficult to obtain the above-mentioned foaming coating material which is applied to the punched metal screen 5 and the cost of the foaming coating material is high.